x立方+2x方-5x-6
=x³-4x+2x方-x-6
=x(x-2)(x+2)+(x-2)(2x+3)
=(x-2)(x方+2x+2x+3)
=(x-2)(x方+4x+3)
=(x-2)(x+1)(x+3)
所以
abc=(-2)×1×3=-6